glitch

A glitch is a sudden change in a pulsar's period and
spin-down rate believed to be caused by a starquake –
the abrupt release of stress energy either in the crust of the star or between
the crust and the superfluid interior. Glitches tend to occur in young pulsars,
such as the Crab pulsar and Vela
pulsar, whose spin rate is decreasing most rapidly.